Processes, microstructure and properties of vanadium microalloyed steels

Abstract

Vanadium as an important alloying element in steels was initially associated with the properties achieved following tempering. Interest in the microstructure was stimulated by the advent of transmission electron microscopes with a resolution of y1 nm together with selected area electron diffraction techniques. A second timely development was that of controlled rolling, particularly of plate and sheet products. The scope of this review will include the historical background on quenched and tempered vanadium steels, precipitation during isothermal aging, conventional controlled rolling and during thin slab direct charging and the development of strength and toughness in vanadium microalloyed steels. The characterisation of microstructure, in particular the methods for the analysis of the chemical composition of precipitates has progressed since the availability of X-ray energy dispersive analysis in the 1970s, and the role played by electron energy loss spectroscopy in providing quantitative analysis of carbon and nitrogen in vanadium microalloyed steels will be presented. There are still many topics involving vanadium microalloyed steels that are controversial. These include the nucleation sequence of homogeneous precipitates of vanadium carbonitride and whether this occurs coherently, the composition of the vanadium precipitates, the nucleation mechanism for interphase precipitation, the importance of strain induced precipitation in austenite of vanadium carbonitride, the contributions of both interphase precipitation and random precipitation in ferrite to the yield strength, and the role of the process route parameters in developing properties. These topics will be considered in this paper which concentrates on hot rolled vanadium microalloyed steels placed in the context of pertinent research on other alloys.

The Effect of the Sintering Temperature and Addition of Niobium and Vanadium on the Microstructure and Mechanical Properties of Microalloyed PM Steels

“…VC, VN and VCN precipitates prevent grain growth in the austenite region and during the austenite-ferrite transformation leading to the formation of small ferrite grains [17]. There are studies in literature arguing that small amounts of vanadium addition to steel increases the nucleation of ferrite grains in grain boundaries and allows for the formation of small ferrite grains [18].…”

“…Especially in the austenite region (900 • C-1300 • C) NbC precipitates formed prevent recrystallization and form small ferrite grains. Niobium and vanadium microalloying elements precipitate as carbide, nitride and carbonitride and contribute to the mechanical properties of microalloyed steels by grain refinement, solid solution precipitation and precipitation hardening mechanisms [17][18][19][20]. Figure 5 shows yield strength (YS), ultimate tensile strength (UTS), elongation and hardness of the examined PM steels.…”

Interphase Precipitation – An Interfacial Segregation Model

“…The steel industry has responded to this challenge by developing single-phase ferritic steels strengthened by interphase precipitation based on various micro-alloying systems. [3][4][5][6] Interphase precipitation consists of periodic rows of carbide precipitates which form simultaneously with the decomposition of austenite and growth of ferrite. 7) The periodicity of these carbide precipitate rows and spacing of precipitates on each respective row strongly influences the mechanical properties through the Ashby-Orowan mechanism.…”

Simulation of Precipitation in v-Containing Hsla Steel for the Strengthening Enhancement

“…Large retained strain together with slow cooling rate is expected to facilitate the precipitation of fine V(C,N) in ferrite and lead to higher strength by the advantage of particle hardening, which is strictly called dispersion hardening [1][2]. They impede the movement of dislocations by the wellknown Orowan-Ashby looping mechanism.…”